Design of a Second-Order Delta-Sigma ADC Based Read/Write Circuit for Memristive Crossbar Arrays

This study introduces a feasible read/write technique applicable to the diverse applications of memristive devices including neuromorphic circuits, logic units, and memory devices. Interest on memristive devices keeps growing in the electronics industry thanks to their nonvolatile property and lower layout density. The proposed readout circuitry is primarily designed for multi-bit logic operations, which enables its use of large-scale biomimicking circuits. The architecture combines bit select decoders, read and write switches for each bit, operational transconductance amplifiers (OTA) connected to readout circuit and an analog-to-digital converter (ADC) to digitalize the signal coming from memristor. Our investigations on various circuit configurations suggest the utilization of a second-order Delta-Sigma ADC operating with an oversampling ratio (OSR) of 256 and a sampling frequency of 128 kHz. An isolation amplifier is utilized to reduce the loading effects between memristor and ADC. As compared to others, the second-order modulator with isolation amplifier demonstrates linear characteristics in multi-bit operations. The whole circuit uses a single type of two-stage opamp design that combines a Miller capacitor and voltage follower in the feedback path for compensation. Overall design works successfully for memristorbased single and multi-bit reading operations.